1. Field of the Invention
The present invention relates to glass ceramic cook top or glass cook top comprising a glass ceramic or glass panel made of pre-stressed special glass, which provides a cooking surface, and an IR-permeable coating made of a heat-resistant inorganic enamel paint, which comprises an inorganic pigment and a glass flux, on the underside of the glass ceramic or glass panel.
2. Description of the Related Art
Cooking ranges with glass or glass ceramic panels acting as cook tops are commercially available in the art. Glass cook tops are typically transparent for visible light, however glass ceramic cook tops are usually translucent. When illuminated from above, e.g. by the cooking unit lighting, or from below, by heat radiation, the heating elements, cables and other structural components, which are hidden below the glass ceramic cooking area, can be observed and show through it. The appearance of these structural elements is considered to be troublesome for the user.
This sort of glass/glass ceramic cook top is typically, as described in EP 0 220 333, colored with color-imparting ions to reduce transmission, so that the operating components under the glass/glass ceramic cook top are not observable from above. These cook tops are thus practically non-transparent for radiation in the visible range and appear to be black.
It is also known to solve this problem by an observation-preventing coating on the underside of the transparent and/or translucent glass and/or glass ceramic cook top. Thus JPH 7-17409 and JP 51-89517 describe glass ceramic cook tops made from a transparent, colorless glass ceramic whose underside is printed with a temperature-resistant paint. This colored paint is thus formed so that the required non-transparency is provided, i.e. it replaces the otherwise conventional coloring, so that the cook top providing the cooking surface appears black when observed.
EP 0 746 179 A2 discloses the use of a covering mask for making a partially non-transparent cook top. However the application of a observation-preventing coating is costly, especially when it occurs by means of screen printing, as in the case of DE 199 06 737 A1.
The observation preventing coating usually consists of a colored lacquer, which contains organic or inorganic pigments. The lacquer adheres to the glass ceramic because of an organic additive provided in the lacquer. Thus the above-described DE 199 06 737 A1 discloses an alkyd resin lacquer for the coating. Luster-imparting paints, sol-gel coatings and noble metal paints are known as the colored lacquers for the observation-preventing coating from DE 100 14 373 A1 and DE 200 19 210 U1. However foils glued to the glass ceramic with silicone (e.g. aluminum foil) are also known. In addition, coatings, which contain no organic ingredients, are known from DE 200 19 210 U1, e.g. comprising a paint made from borosilicate glass as glass flux and titanium or cerium oxide as pigment.
Organic based paints are used almost exclusively for observation-preventing coatings of the underside of glass/glass ceramic cook tops in practice, glass ceramic cook top. The disadvantage of these organic paints is that they have only limited heat-resistance because of their organic composition. Typical ingredients, such as silicones, polyesters or resins, decompose at temperatures above 400° C. However in operation the underside of the cook top of cooking ranges reaches up to 600° C. The organic paints decompose generally under heat load and the adherence of the coating is lost over time.
Of course the paint made from borosilicate glass flux and titanium or cerium oxide as pigments disclosed in the above-described DE 200 19 210 U1 has the required temperature-resistance. However the strength of the glass ceramic cook top is clearly reduced because of differing thermal expansion coefficients and the mechanical stresses thereby produced. Furthermore the resulting coating is not observation preventing or view blocking.